1. Field of Invention
This invention relates to copper-base alloys and, more particularly, to homogeneous, ductile brazing filler metal alloys useful for joining steels, cemented carbides to steels, copper to steels, copper to copper and copper alloys, and composite materials to steels and copper.
2. Description of Prior Art
Three basic types of filler metals are conventionally used to join ferrous and non-ferrous alloys. According to specifications for brazing filler metals published in 1976 by the American Welding Society, these three major groups are classified as follows:
1. BAg classifications--Filler metals having this classification are used mainly for brazing carbon and low alloyed steel. These alloys have good wetting characteristics and braze steels well at relatively low temperatures, thereby minimizing grain growth in steel during brazing. These alloys do not contain phosphorus and, therefore, brazed joints exhibit good ductility because of the absence of brittle phosphides. However serious disadvantages exist in the applications; namely, they usually contain substantial amounts of toxic cadmium and precious silver.
2. BCu classifications--Filler metals having this classification are used mainly in furnace brazing in controlled atmospheres at temperatures exceeding 1000.degree. C. (1850.degree. F.). This group consists of alloys which have compositions with copper concentration exceeding 99%. Obviously these alloys cannot be used at low temperatures or under open atmospheric conditions.
3. RBCuZn classifications--Filler metals having this classification are used primarily at brazing temperatures exceeding 925.degree. to 950.degree. C. (1700.degree. to 1740.degree. F.). In ferrous brazing applications the major disadvantage of the last two classifications is a high brazing temperature. It is well known that such high temperature exposure causes austenite grain growth leading to the appearance of retained austenite which, in turn, results in increased warpage and other deleterious effects.
Attempts have been made to develop new alloy alternatives to the BAg alloys. These new alloy alternatives are based on a copper-manganese system which has a few low melting eutectic compositions. Modified copper-manganese alloys contain small amounts of various elements used as melting temperature depressants and/or strengthening agents.
British Pat. No. 996,177 published on June 23, 1965, describes a nickel-copper-manganese alloy containing small amounts of boron and germanium as temperature depressants in addition to iron and silicon. All alloys disclosed therein have melting temperatures well above 875.degree. C. (1000.degree. F.).
U.S. Pat. No. 4,071,538 describes a copper base brazing alloy containing manganese, nickel, tin and indium. The brazing temperature for this alloy is in the range of 1000.degree.-1050.degree. C. (1836.degree.-1925.degree. F.) which is much higher than temperatures acceptable for ferrous and copper brazing.
U.S. Pat. No. 4,357,299 describes a copper-base brazing alloy containing substantial amounts of manganese with small additions of nickel, iron, indium and tin which is suitable for brazing cemented carbide to steel. All of the alloys disclosed therein, have melting temperatures higher than 820.degree. C. No mention is made therein concerning brazing of materials other than SAE 4340 steel-cemented carbide.
Japanese Kokai Patent Publications No. 165590 and No. 165591 describe copper-manganese base alloys used as brazing filler materials at brazing temperature well above 900.degree. C. Those alloys, in addition to copper and manganese, contain at least one of zinc, nickel, iron and cobalt, together with silver, aluminum, indium and rare earth elements. No data concerning mechanical properties of joints brazed with these materials is disclosed therein and the alloys are claimed to have utility in joining cemented carbide tool tips to their steel holders.
Each of the aformentioned patents teaches fabrication of the brazing filler metal by conventional processes which comprise the steps of melting, ingot casting and subsequent multiple stage deformation. The microstructures of these alloys are heterogeneous, resulting in relatively coarse joint microstructure.
There still remains a need in the art of joining ferrous and non-ferrous metals to develop new brazing filler metals that have low melting points, are homogeneous and contain little or no precious metals (e.g. silver) or toxic elements (e.g. cadmium).